Sensorimotor Control of Behavior:

Somatosensation

Lecture 8

Somatosensation

Sensory info from body Cutaneous senses

exteroceptors touch / pain

Kinesthesia interoceptors body position & movement ~

Somatosensory cortex

S1 - Postcentral Gyrus Somatotopic Organization

topographic representation of body Distorted Homunculus

disproportionate amount of cortex for body parts

high sensitivity: large cortical area ~

Somatosensory Cortex

Formation of a Body Image Does not simply respond to

sensory input Phantom Limbs

after amputation also pain ~

M1S1PPC

Kinesthesia

Kinesthesia

Body Position & Movement proprioception

Joint information Pacinian corpuscles & Ruffini endings

Muscle & tendon information changes in tension

Golgi tendon organ

muscle spindle fibers ~

Cutaneous Receptors

Stretching of the skin Limited role in proprioception

Ruffini Endings slow adapting population of neurons responding

simultaneously ~

Cutaneous Receptors

Role depends on location Anesthetize skin assess ability to detect passive

movement Knee: no affect on proprioception Mouth, hands, & feet

proprioception significantly reduced ~

Muscle Receptors

Major role in proprioception Stretch receptors

detect changes in tension 2 types of receptors

Muscle spindles & Golgi tendon organs differences in threshold & location ~

Muscle length detectors Parallel with extrafusal fibers Low threshold

Monosynaptic stretch reflex Postural adjustments Muscle tonus

Sensory neuron ---> alpha motor neurons

monosynaptic excitation

disynaptic inhibition ~

Muscle-Spindle Receptors

Dorsal

Ventral

++

MS

-

+

+

Golgi Tendon Organ

Gauges muscle tension high threshold

Stretch receptor safety mechanism controlled muscle contraction ~

Dorsal

Ventral

-+

GTO

+Inhibits alphamotor neuron

GTO: Function

Inhibits muscle contraction Control of motor acts

slow contraction as force increases e.g., holding an egg

breaks if too much force Autogenic inhibition

safety mechanism too much tension ---> damage ~

The Orienting Senses

Orientation: The Vestibular System

Position & motion of body in space critical for adaptive interaction largely unnoticed except unusual conditions

motion sickness: nausea, dizziness Maintenance of balance & posture

coordinating body position with other sensory information ~

Receptors for Orientation

Inner ear Gravity detectors

plane of reference Mechanoreceptors Vestibular Organs

otocysts• saccule• utricle

semicircular canals ~

Otocysts

Liquid-filled “ear sacs” lined with hair cells contain otoliths

“ear stones : direction of acceleration

saccule: vertical movement utricle: horizontal movement ~

At rest tiltedAcceleration to right

Direction of gravity

Acceleration to right

Semicircular Canals

Rotary acceleration direction & extent of circular movement

any direction 3 fluid-filled canals

right angles to each other 1 for each major plane

Movement causes fluid to circulate displaces cupula ~

Semicircular canals

UtricleAmpulla

Cristahair cells

Cupula

Vestibular Pathway

Vestibulocochlear nerve (VIII) Some axons directly to cerebellum Most axons to medulla

vestibular nuclei cerebellum, spinal cord, medulla & pons motor nuclei for eyes (III, IV, & VI)

compensates for movement of head temporal cortex (dizziness) ~

Input to Vestibular System

Other sensory informationeyes

trunk & neck

limbs

cerebellum Constant postural adjustments

Maintains visual image fixed on retina maintains center of gravity during movement

~

Sensorimotor Integration

Sensorimotor Integration

Somatosensory cortex provides spatial coordinates

Motor Cortex executes movements

Results in meaningful behavior ~

Posterior Parietal Cortex - PPC

Constructs spatial coordinates for behavior

Apraxia inability to purposefully organize

movements Left parietal apraxia

bilateral inability to perform requested movements ~

Constructional apraxia - damage to PPC

Spatial Neglect

Contralateral neglect neglect of left side of body and world

Damage to right PPC map of body & space destroyed ~